Hybrid type powertrains generally employ an internal combustion engine and one or more motor/generator units that operate in concert to provide driving power to the wheels of a vehicle. The electric portion of the vehicle is generally used where noise or exhaust emissions are of prime concern. This type of vehicle is suited for operation in a closed environment (electric drive), such as a passenger terminal, and an open environment (engine drive) such as a parking structure. Thus the vehicle is ideal for transporting passengers from a terminal to a parking structure.
Vehicles employing a hybrid powertrain are also well suited for urban transportation where a significant amount of stop and go driving is undertaken. These vehicles propose electrical regenerative braking to recharge the electrical power storage devices (batteries). During urban travel the powertrain takes advantage of both the internal combustion engine and the electric drive to improve both fuel economy and exhaust emissions. The hybrid powertrain permits the engine to be shut-off at vehicle stops. Restart and or vehicle acceleration is attended to by the electric drive.
The hybrid powertrains are also suited for over-the-road transportation where the electric drive units can be utilized to assist in driving the vehicle during high-power output conditions such as rapid acceleration and hill climbing. The electric drive units might also provide propulsion in the event that engine operation is inadvertently discontinued.
In all of the electro/mechanical hybrid powertrains, the electrical and mechanical drive units are designed to operate in all of the vehicle driving conditions. Also the powertrains generally include planetary type gearing which is designed to effectively combine the electrical and mechanical drive units into an integrated system.
It has been proposed in some systems to position the electric drive between the engine and the transmission. These systems have been termed Flywheel-Alternator-Starter (FAS) systems. The FAS system increases the transmission size in a longitudinal direction and often requires additional radial space. In some FAS systems, for example the U.S. Pat. Nos. 5,258,651 (issued Nov. 2, 1993); 5,285,111 (issued Feb. 8, 1994).to Sherman, the motor/generator and a planetary gear arrangement replace the more conventional torque converter.